Lambda Type References

Posted by & filed under Java.

We’re used to type erasure ruining our day in Java. Want to create a new T() in a generic method? Normally not possible. We can pass a Class<T> around, but that doesn’t work for generic types. We can’t write List<String>.class One exception to this was using super type tokens. We can get the generic type… Read more »

Yield Return in Java

Posted by & filed under c#, Java.

A feature often missed in Java by c# developers is yield return It can be used to create Iterators/Generators easily. For example, we can print the infinite series of positive numbers like so: public static void Main() { foreach (int i in positiveIntegers()) { Console.WriteLine(i); } }   public static IEnumerable<int> positiveIntegers() { int i… Read more »

Adding toList() to Java Streams

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The Java Streams API is lovely, but there are a few operations that One repeats over and over again which could be easier. One example of this is Collecting to a List. List<String> input = asList("foo", "bar"); List<String> filtered = input .stream() .filter(s -> s.startsWith("f")) .collect(Collectors.toList());List<String> input = asList("foo", "bar"); List<String> filtered = input .stream()… Read more »

Work around Java “same erasure” errors with Lambdas

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A common frustration with Java is the inability to overload methods when the method signatures differ only by type parameters. Here’s an example, we’d like to overload a method to take either a List of Strings or a List of Integers. This will not compile, because both methods have the same erasure. class ErasureExample {… Read more »

Implicit Conversions with Identity Functions

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What use is a method that just returns its input? Surprisingly useful. A surprising use is as a way to convert between types. There’s a well known trick that’s often used to work around Java’s terrible array literals that you may have come across. If you have a method that takes an array as an… Read more »

Builder Pattern with Java 8 Lambdas

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The builder patten is often used to construct objects with many properties. It makes it easier to read initialisations by having parameters named at the callsite, while helping you only allow the construction of valid objects. Builder implementations tend to either rely on the constructed object being mutable, and setting fields as you go, or… Read more »

Frameworkless Dependency Injection

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Twice recently we have had “fun” trying to get things using HK2 (Jersey), to place nicely with code built using Guice and Spring. This has renewed my appreciation for code written without DI frameworks. The problem with (many) DI frameworks. People like to complain about Spring. It’s an easy target, but often the argument is… Read more »

Deep Pattern Matching in Java

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This is a follow up to Pattern matching in Java, where I demonstrated pattern matching on type and structure using Java 8 features. The first thing most people asked is “does it support matching on nested structures?” The previous approach did not, at least not without creating excessive boilerplate constructors. So here’s another approach that… Read more »

Tuples in Java

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The absence of tuples in Java is often bemoaned. Tuples are collections of a variety of types. They might look like (“benji”,8,”weber”) – a 3-tuple of a string, a number, and another string. People often wish to use tuples to return more than one value from a method. Often this is a smell that we… Read more »

JSON to Java Interfaces with Nashorn

Posted by & filed under Java, JavaScript.

Here’s a neat trick to transform JSON into Java objects that implement an interface with the same structure. Java 8 comes with Nashorn – a JavaScript runtime that has a number of extensions. One of these extensions allows you to pass a JavaScript object to a constructor of an interface to anonymously implement that interface…. Read more »